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Chengming Zhou e5c0ca1365 blk-mq: release scheduler resource when request completes 
Chuck reported [1] an IO hang problem on NFS exports that reside on SATA
devices and bisected to commit 615939a2ae ("blk-mq: defer to the normal
submission path for post-flush requests").

We analysed the IO hang problem, found there are two postflush requests
waiting for each other.

The first postflush request completed the REQ_FSEQ_DATA sequence, so go to
the REQ_FSEQ_POSTFLUSH sequence and added in the flush pending list, but
failed to blk_kick_flush() because of the second postflush request which
is inflight waiting in scheduler queue.

The second postflush waiting in scheduler queue can't be dispatched because
the first postflush hasn't released scheduler resource even though it has
completed by itself.

Fix it by releasing scheduler resource when the first postflush request
completed, so the second postflush can be dispatched and completed, then
make blk_kick_flush() succeed.

While at it, remove the check for e->ops.finish_request, as all
schedulers set that. Reaffirm this requirement by adding a WARN_ON_ONCE()
at scheduler registration time, just like we do for insert_requests and
dispatch_request.

[1] https://lore.kernel.org/all/7A57C7AE-A51A-4254-888B-FE15CA21F9E9@oracle.com/

Link: https://lore.kernel.org/linux-block/20230819031206.2744005-1-chengming.zhou@linux.dev/
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202308172100.8ce4b853-oliver.sang@intel.com
Fixes: 615939a2ae ("blk-mq: defer to the normal submission path for post-flush requests")
Reported-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Tested-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/20230813152325.3017343-1-chengming.zhou@linux.dev
[axboe: folded in incremental fix and added tags]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2023-08-19 07:47:17 -06:00
arch Scope-based Resource Management infrastructure 2023-07-04 13:50:38 -07:00
block blk-mq: release scheduler resource when request completes 2023-08-19 07:47:17 -06:00
certs
crypto
Documentation More power management updates for 6.5-rc1 2023-07-04 11:22:50 -07:00
drivers drivers/rnbd: restore sysfs interface to rnbd-client 2023-08-18 15:00:39 -06:00
fs afs: Fix accidental truncation when storing data 2023-07-04 12:24:32 -07:00
include block: don't make REQ_POLLED imply REQ_NOWAIT 2023-08-09 16:04:07 -06:00
init
io_uring io_uring-6.5-2023-07-03 2023-07-03 18:43:10 -07:00
ipc
kernel module: fix init_module_from_file() error handling 2023-07-04 10:17:11 -07:00
lib sbitmap: fix batching wakeup 2023-07-21 11:40:20 -06:00
LICENSES
mm gup: make the stack expansion warning a bit more targeted 2023-07-05 09:33:31 -07:00
net
rust
samples Char/Misc and other driver subsystem updates for 6.5-rc1 2023-07-03 12:46:47 -07:00
scripts Scope-based Resource Management infrastructure 2023-07-04 13:50:38 -07:00
security Scope-based Resource Management infrastructure 2023-07-04 13:50:38 -07:00
sound
tools virtio: features, fixes, cleanups 2023-07-03 15:38:26 -07:00
usr
virt ARM64: 2023-07-03 15:32:22 -07:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore Revert ".gitignore: ignore *.cover and *.mbx" 2023-07-04 15:05:12 -07:00
.mailmap
.rustfmt.toml
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS power supply and reset changes for the 6.5 series 2023-07-03 17:23:16 -07:00
Makefile Scope-based Resource Management infrastructure 2023-07-04 13:50:38 -07:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.